1. Field of the Invention
This invention relates to a packaging bag for the sheet for electrophoresis composed of a gel membrane for electrophoresis and two sheets of the support supporting the gel membrane from both sides.
2. Description of Prior Art
The electrophoretic operation is known to separate charged molecules or particles such as proteins, their hydrolyzates, nucleic acids and their hydrolyzates by utilizing the phenomenon that they migrate in a sheet medium such as gel membrane or filter paper impregnated with a pH buffer by loading an electric filed. This electrophoretic operation is utilized for the separation and identification of the above biopolymers and the like.
Besides, in the field of genetic engineering, electrophoretic operation is used, for example, in order to determine the base sequence of nucleic acid such as DNA by utilizing autoradiography. In general, the electrophoretic operation for this purpose contains the operation where two or more kinds of base-specific reacting species of DNA or DNA fragments labeled with radioisotope are allowed to migrate in parallel along the direction of the electric field of the medium for electrophoresis. The electrophoretic patterns obtained as autoradiogram (the aggregate of zones formed on the medium by the electrophoresis) are compared with each other to determine the base sequence. This comparison utilizes the principle of the electrophoresis that the base-specific reacting species having the same molecular weight migrate to the same position when their starting points are the same.
The medium for electrophoresis is usually filter paper, membrane filter, starch gel membrane, polyacrylamide gel membrane or the like, and it is a sheet having an uniform thickness. In the past, the gel membrane such as starch gel membrane or polyacrylamide gel membrane was prepared by pouring the solution for forming gel membrane into the frame put on a support made of a nonconductive material such as glass plate. Then, another support plate was put thereon, and allowed to stand to form the gel membrane. However, this preparation work was troublesome, and moreover, the gel membrane was sometimes damaged at the time of removing the glass plate prior to the operation of autoradiography.
As the means of solving these problems, a gel membrane hard to be damaged has been disclosed (Japanese Patent KOKAI No. 59-126236). Besides, an easily usable sheet for electrophoresis (Japanese Patent KOKAI No. 59-126237) and its preparation method (Japanese Patent KOKAI No. 60-203847) have also been disclosed. This sheet for electrophoretsis is, as shown in FIG. 12, composed of two gel membrane support sheets 12, 12 disposed at a prescribed interval through a spacer 13 and a gel membrane for electrophoresis 14 formed between the support sheets 12,12. The support sheets are made of nonconductive organic polymer film. As shown in FIG. 7, a slot 11 is provided over the whole upper edge of the gel membrane 14, and many recesses 15 for receiving samples are formed in a row at its bottom. Such an electrophoretic sheet has been developed for mass production, and accordingly it is necessary to be protected so as not to deteriorate its quality during storage. While, the polyacrylamide solution for the preparation of polyacrylamide gel membrane contains 63 grams of urea in 150 ml of the solution. The preparation method of polyacrylamide gel membrane for electrophoresis is described in "Manual of DNA Sequence Analysis" (Ed. by M. Takanami et al, p 49 -, Kodansha, Japan). This content is near the saturation of urea. Therefore, when water evaporates from the polyacrylamide gel membrane, urea in the gel deposits in a short time. The deposition occurs particularly at the part of the slot. Thus, it is necessary to prevent the water evaporation during storage.
The present inventor has investigated in order to obtain a suitable packaging material for the gel membrane for electrophoresis capable of preserving without the deterioration of quality. For example, the packaging material of FIG. 9 is composed of high-pressure branched low-density polyethylene (LDPE) resin layer 7 having a thickness of 100 .mu.m or 200 .mu.m. The packaging bag made of this packaging material was not suitable for the gel membrane for electrophoresis, because urea deposited during the storage within one year. The packaging material of FIG. 10 is composed of a thermoplastic resin layer 2, an aluminum foil layer 8 laminated thereon through an adhesive layer 3, and a paper layer 9 further laminated thereon through an adhensive layer 3. Using this packaging material, the bag 4 shown in FIG. 11 was made. All side edges 10 of this bag 4 were heat-sealed. The moistureproofness of this bag is good, but the gel membrane in the bag cannot be inspected because of invisibility. When the bag was opened by a scissors, the gel membrane was occasionally cut together with the bag because its inside could not be seen. The curling of this packaging material was large, and the insertion of the gel membrane was bad. The blocking of the packaging material was also a problem, and moreover, it was expensive.